1. Field of Invention
The present invention relates to a fuel vapor control apparatus that prevents fuel vapor generated in a fuel tank of an internal combustion engine from being directly discharged into the atmosphere at the time of fuel supply and, more particularly, to an improved fuel vapor control apparatus that prevents a deterioration in operating characteristics of a fuel vapor control valve by returning fuel accumulated in the fuel vapor control apparatus to the fuel tank.
2. Description of Related Art
As a system for preventing fuel vapor generated in a fuel tank from being discharged into the atmosphere at the time of fuel supply by using a canister for adsorbing such fuel vapor, there is a fuel tank control system disclosed in Japanese Patent Application Laid-Open No. HEI 8-276757, which will now be described with reference to FIG. 9.
Referring to FIG. 9, a fuel tank 31 is connected with a canister 32 for adsorbing fuel vapor through a line 33, which is provided with a fuel vapor control apparatus 34. If the pressure of fuel vapor generated in the fuel tank 31 at the time of fuel supply reaches a predetermined set level, a fuel vapor control valve 34A installed in the fuel vapor control apparatus 34 is opened due to a difference in pressure, so that the fuel vapor flows into the canister 32. The fuel vapor is then adsorbed by an adsorbent contained in the canister 32 and temporarily stored therein. Upon start of an internal combustion engine, the fuel vapor that has been adsorbed by the canister 32 is sucked together with outside air, which is sucked into an outside air inlet 35 formed in the canister 32 due to a negative pressure generated in an intake pipe. The fuel vapor flows through a purge pipe 36 and the intake pipe and reaches cylinders of the internal combustion engine.
The aforementioned fuel vapor control apparatus operates as follows at the time of fuel supply.
When a filler cap 37 is opened to supply fuel, the atmospheric pressure is supplied to an upper chamber of the fuel vapor control apparatus 34 through a line 39 leading to a filler pipe 38, whereas the supply of fuel results in a rise in pressure in the fuel tank 31. Due to a difference in pressure between the upper chamber and the fuel tank 31, the fuel vapor control valve 34A of the fuel vapor control apparatus 34 is opened, so that fuel vapor flows through the line 33 and is stored in the canister 32. Thus, the fuel vapor is not discharged into the atmosphere through the filler pipe 38.
If a vehicle equipped with the fuel vapor control valve 34A of the fuel vapor control apparatus 34 of such a structure turns or is inclined, liquid fuel flows back through the filler pipe 38 and the line 39 and enters the upper chamber of the fuel vapor control valve 34A, so that there is a possibility of the liquid fuel being accumulated in the upper chamber of the fuel vapor control valve 34A.
With a view to preventing such accumulation of fuel, the aforementioned fuel vapor control apparatus adopts a structure wherein a communication hole 41 as a fuel drop passage is formed in the fuel vapor control valve 34A of the fuel vapor control apparatus 34.
Referring to FIGS. 10 and 11, the fuel vapor control valve 34A of the fuel vapor control apparatus 34 is composed of a diaphragm, which has the communication hole 41 formed in the vicinity of the center thereof. A guide piece 42 is disposed upright around the communication hole 41. A casing constituting the fuel vapor control apparatus 34 is provided with a closure member 43 fitted into the guide piece 42. The communication hole 41 is closed by an end 43A of the closure member 43 when the fuel vapor control valve 34A achieves a maximum upward lift amount due to a difference in pressure.
The fuel vapor control apparatus 34 is designed such that the fuel accumulated on the fuel vapor control valve 34A is returned to the fuel tank 31 through the communication hole 41. Thus, the operating characteristics of the fuel vapor control valve 34A are free from a deterioration due to a weight of the fuel accumulated on the fuel vapor control valve 34A.
Furthermore, since the communication hole 41 is closed by the end 43A of the closure member 43, there is no possibility of the fuel vapor generated in the fuel tank at the time of fuel supply being discharged into the atmosphere through the communication hole 41 and the filler pipe 38.
However, the communication hole 41 of the aforementioned fuel vapor control apparatus 34 has a structural drawback, which will hereinafter be described.
As can be seen from FIG. 10, there is a gap H formed between the fuel vapor control valve 34A and the end 43A of the closure member 43. Thus, at the time of fuel supply, the fuel vapor control valve 34A rises in height by the gap H due to a difference in pressure, so that the fuel vapor in the fuel tank 31 flows through the communication hole 41 prior to closure thereof. For this reason, the operating characteristics of the fuel vapor control valve 34A deteriorate and the fuel vapor that has flown through the communication hole 41 enters the filler pipe 38 through the line 39, whereby a small amount of fuel vapor is discharged into the atmosphere.